BP Sold Control of Castrol to Strengthen Its Balance Sheet. Then an Oil Windfall Complicated the Timing

On 30 October, BP reported net debt of $13.87 billion, down from $22.25 billion at the end of June. In February 2025 the company had set itself a target of $14 billion to $18 billion by the end of 2027. It had slipped under the bottom of that range more than a year early.

Three days later, on 2 November, BP completed the sale of a 65% stake in Castrol to Stonepeak. The roughly $6 billion BP receives after tax was not in the October figure. The Castrol sale was meant to carry BP toward its debt target, and the target was reached before the money arrived.

That does not make the sale a mistake. It does make it harder to judge than the closing-day press releases suggest. BP agreed the deal on 24 December 2025, when its last reported net debt was $26.1 billion and Brent crude was trading in the low $60s. The war in Iran, the closure of the Strait of Hormuz and an extraordinary refining quarter all came after the signature. What follows keeps the two periods apart: what BP knew when it sold, what it sold and what it kept, and what the next few years will show.

Why did BP decide to sell 65% of Castrol?

BP's stated reasons are a stronger balance sheet and a simpler downstream business built around assets that fit its integrated model. The decision has a paper trail. On 26 February 2025, BP announced a reset of its strategy. Oil and gas investment would rise to about $10 billion a year, spending on transition businesses would fall to between $1.5 billion and $2 billion a year, and the company would sell $20 billion of assets by the end of 2027. The same announcement opened a strategic review of Castrol, and BP said any proceeds would go toward reducing net debt.

So the December agreement came ten months into a process BP had announced in public. The financial backdrop explains why the process mattered. BP describes 2025 as a weaker price environment, and its numbers show it: underlying replacement-cost profit for the year was $7.5 billion, down from $8.9 billion in 2024, and operating cash flow was $24.5 billion against $27.3 billion. Net debt ended 2025 at $22.2 billion, helped by about $3.6 billion of disposal proceeds in the fourth quarter, and still well above target.

When BP published those results in February 2026, its board suspended share buybacks. Management added that reaching the debt target would not automatically bring them back. BP's guidance at the time was that net debt would rise in the first half of 2026 and fall sharply in the second as disposal proceeds arrived, with Castrol the largest single piece.

Three executives touched the transaction. The reset was announced under Murray Auchincloss, the Castrol agreement under interim chief executive Carol Howle, and the closing under Meg O'Neill, who took over on 1 April. That is a good reason to treat this as a company decision rather than one leader's call.

Why 65% and not the whole company is less well documented. BP has said the retained stake keeps it exposed to Castrol's growth plans, and that is the extent of the stated reasoning. It has not set out the alternatives it weighed, such as a full sale or a public listing, so any account of why this structure won is inference.

What did BP actually get for $10.1 billion?

The headline number is an enterprise value of $10.1 billion, which BP puts at about 8.6 times Castrol's earnings before interest, tax, depreciation and amortisation over the previous twelve months. Enterprise value is not cash. BP's own bridge takes off $1.8 billion of minority interests held by partners in India, Vietnam, Saudi Arabia, Thailand and other markets, plus about $0.3 billion of other debt-like obligations, which leaves an equity value of roughly $8 billion.

Stonepeak bought 65% of that equity. As an illustration, 65% of $8 billion is $5.2 billion, and most of the distance to BP's $6 billion comes from a different item: about $0.8 billion BP received in advance for dividends it would otherwise have collected later on the stake it kept. This is the writer's arithmetic, not a reported breakdown. BP quotes its final figure after tax and what it calls customary adjustments. It still shows the shape of the deal. Part of the $6 billion is cash today in exchange for income tomorrow, so the 65% itself fetched less than the headline implies.

The minority interests matter for another reason. Castrol's EBITDA is a whole-business figure, and part of the profit beneath it belongs to partners. BP says the partners' share of net income averaged about $100 million a year between 2019 and 2025. That does not distort the 8.6 times multiple, since enterprise value and EBITDA are both measured for the whole business. What it changes is how much of the $10.1 billion BP could ever have called its own, which is why the equity bridge tells you more than the headline.

What the 35% stake pays, and what it does not

BP kept 35% and has the option to sell it after a two-year lock-up. It will account for the holding as an equity investment. BP has said it does not expect to book earnings from it or receive a dividend in the short to medium term, because Stonepeak has a preference on distributions. A 35% stake would normally suggest a 35% share of profits. Here, the preference means Stonepeak is paid first.

Control sits elsewhere too. Castrol now has a ten-member board: four independent directors including the chair, Ben van Beurden, the former chief executive of Shell, three directors tied to Stonepeak, two from BP and one representing CPP Investments. Stonepeak, an infrastructure-focused investor, manages about $98 billion as of June 2026. BP describes Castrol as a standalone company with its own management, governance and strategic priorities. Michelle Jou remains chief executive.

Read plainly, the retained stake is closer to an option on Castrol's growth than an income stream. Its value depends on how fast Castrol grows under owners who rank ahead of BP for cash, and on the price BP can later achieve if it chooses to sell.

A business that was still growing

BP bought Castrol in 2000 for £3 billion. It then served customers in about 50 countries; BP now puts the figure above 150, and the product range has stretched from engine oil into electric-vehicle fluids and cooling for data centres. BP's adjusted EBITDA for the business rose from about $897 million in 2023 to $1.007 billion in 2024 and $1.15 billion in 2025. BP reported that Castrol's 2025 earnings grew by more than 15%, with ten consecutive quarters of year-on-year growth. BP did not unload a failing business. It sold a growing one, partly because a growing business is what buyers pay for.

The 2026 figures need care. Castrol's EBITDA for the first nine months of 2026 was $1.06 billion, against $888 million a year earlier, an increase of about 19%. In the third quarter alone it was $285 million, down from $309 million a year before. BP had warned in its second-quarter report that the lagged effect of higher base oil costs would weigh on Castrol's earnings in the third quarter, so the dip was flagged in advance. One quarter is not a trend.

Profit comparisons are trickier. BP's underlying replacement-cost profit before interest and tax for Castrol was $1.06 billion for the nine months of 2026, against $744 million a year earlier, which looks like growth of about 42%. The two profit figures matching exactly for 2026 is the clue: depreciation stopped once Castrol was classed as held for sale, and BP itself notes the lower depreciation. EBITDA, which ignores depreciation, is the like-for-like measure, and it says 19%. Castrol's earnings will also leave BP's results now that the sale has closed, and BP guided in October to lower Castrol earnings in the fourth quarter, subject to completion. Part of the fall in BP's reported Castrol numbers will be the sale itself.

How 2026 changed the picture

The US-Israeli war with Iran began on 28 February 2026. The Strait of Hormuz was all but closed in March, and Brent reached $119.50 a barrel during trading on 9 March, its highest since mid-2022. Brent averaged $81.13 in the first quarter, against $63.73 in the fourth quarter of 2025. Nothing in BP's December announcement could have priced that in, and it would be unfair to read the sale as if it had.

The first effect on BP's balance sheet was unhelpful. Net debt rose to $25.3 billion at the end of March, from $22.2 billion at the end of 2025, as higher prices tied up working capital. At 30 June it was $22.25 billion, almost exactly where the year began. By August BP was saying it expected to reach its target range ahead of schedule, though its finance chief added that further reduction would be needed. Through the first half, nothing had yet removed the case for selling.

The third quarter did. Brent averaged $96.99 and BP's refining indicator margin reached $46.70 a barrel, up from $29.60 in the second quarter. Underlying replacement-cost profit was $8.5 billion, against $2.2 billion a year earlier, and operating cash flow was $14.8 billion. Net debt fell by $8.4 billion in the quarter, even after BP repaid $1 billion of hybrid securities. BP's chief executive said the results were helped by the higher-price, higher-margin environment. The company also booked $4 billion of post-tax impairments, largely on its transition businesses.

None of that is credit to the Castrol sale, which closed after the quarter ended. Nor should it be read as a new baseline. A refining quarter like that one depends on the disruption that produced it.

Net debt is also a narrower yardstick than it sounds. BP tracks a wider measure that adds hybrid securities, lease liabilities and Gulf of America settlement liabilities, and that figure fell by $9.3 billion from the second quarter. The company's own verdict on the quarter was restrained: it called the progress good, said it was still too leveraged, and described further strengthening of the balance sheet as its number one job.

The decision can be read two ways. One holds that BP sold when it needed to, in conditions it could see, and that a windfall which let it hit the target early should not rewrite the decision. The other counts what BP now would not have needed. It reached its 2027 debt target without Castrol's proceeds, at least for one quarter of exceptional prices, having given up majority control of a business earning more each year. Each is defensible. They differ on whether a decision is judged by what was known at signing or by how things turned out. The first is the better standard, but the second explains why the question is still open.

What will decide whether the sale was right

The first test is what BP does with the room it created. BP has framed the roughly $6 billion as further strengthening of the balance sheet, on top of a net debt figure already below target. It suspended buybacks in February and had not restarted them by its third-quarter results. It has scheduled a strategy and outlook update for 15 December in New York. Its contents are not public, and how far it departs from the February 2025 reset will not be known until it is published.

The second is whether the oil market keeps paying. If prices ease and refining margins fall back toward last year's levels, the deleveraging the sale delivered will matter more than it does today. If they stay high, the sale will look in hindsight like an expensive way to reach a position BP was about to reach anyway.

The third is Castrol itself. BP gave up control of the business and kept a stake that pays nothing for now. If Castrol keeps growing under Stonepeak and BP eventually sells its 35% for a good price, the structure will look clever. If growth stalls, or distributions stay with Stonepeak for longer than expected, BP will have sold the larger share of a good business and held the smaller one with little to show for it. The base oil cost squeeze that dented the third quarter is a reminder that Castrol's margins move with inputs its owners do not control.

Until the December update, the record shows this much. BP sold a growing business to address a balance-sheet problem, and by the time the proceeds arrived its headline net debt target had already been met, although BP itself says the wider job is unfinished. Whether that was prudence or awkward timing depends partly on how long the oil market keeps covering BP's bills.