A survey of pension disclosures for companies in London’s FTSE 100 index found that as of June 30 these companies had a combined pension deficit of around £17 billion — and Anglo-Dutch oil group Royal Dutch Shell had the largest defined-benefit-pension deficit of any of these companies in 2016, after its deficit grew by nearly 140 percent from the previous year.

Investment consultant LCP, which released the results of its 24th annual Accounting for Pensions survey on Wednesday, found that Royal Dutch Shell’s defined-benefit-plan deficit grew from £2.9 billion ($3.8 billion) in 2015 to £6.9 billion in 2016. Shell did not respond to a request for comment.

The LCP research analyzed 89 defined benefit schemes of the U.K.’s largest listed companies. Eleven companies were excluded from the analysis, as they do not sponsor a defined-benefit-pension scheme. The report found that over the past decade, FTSE 100 companies paid £150 billion into their defined benefit schemes, and asset values have risen from £350 billion in 2007 to more than £600 billion today. Yet the FTSE 100 companies surveyed still have a combined pension deficit.

[II Deep Dive: Goldman: Small U.K. Pension Plans See Widest Funding Gaps]

“The reason for this is that liability values have grown even more quickly,” the report stated, noting that these values have risen more than 85 percent, to £625 billion, over the same period.

While the LCP report put Shell’s scheme’s deficit as larger than that of rival BP, the latter’s deficit also grew between 2015 and 2016. BP had a shortfall of £6.7 billion, up more than 59 percent from the £4.2 billion deficit it had in 2015. BP had the second-largest defined-benefit-scheme deficit in this year’s survey.

“Globally BP operates both funded and unfunded plans,” a BP spokeswoman said in a statement responding to the report. (Unfunded defined-benefit-pension plans use an employer’s current income to fund pension payments as they are needed.) “Our annual report gives the global position, not just the U.K., and includes both our funded and unfunded plans. By definition, unfunded plans are not designed to be funded, and their liabilities are reported as a deficit.”

In 2007, FTSE 100 defined benefit schemes boasted a combined £12 billion surplus, but by 2017 that had swung to the £17 billion deficit reported by LCP. Despite this, some schemes have been successful in reducing their deficits over the past year.

Telecom giant BT, which at £7.6 billion had the largest deficit in last year’s LCP report, reduced its deficit by 15.8 percent in 2016, to £6.4 billion. A spokeswoman for the BT Pension Scheme declined to comment as to the reasons. Supermarket chain Tesco reduced its deficit by about a third between 2015 and 2016, from £4.8 billion to £3.2 billion.

Alan Baker, head of defined benefit solutions development at Mercer, tells Institutional Investor that the level of hedging that FTSE 100 retirement plans embraced ultimately had a notable impact on funding levels between 2015 and 2016.

“Hedging is an expensive business, and for some large companies it isn’t entirely practical to hedge all of those liabilities,” he says. “Those that hedged have weathered things well.”

Dan Mikulskis, head of defined benefit pensions at U.K.-based investment consultant Redington, says that according to the PPF 7800 index, aggregate funding levels of defined benefit schemes have improved since mid-June 2016. The PPF 7800 index tracks the estimated funding positions for defined benefit schemes in the Pension Protection Fund’s eligible universe. The PPF compensates eligible employees when an employer becomes insolvent or has insufficient assets to pay benefits.

“The continued uncertainty over future economic conditions and the persistent low interest rates continue to highlight the importance of risk management to pension scheme outcomes,” he says.