Shell's UK managing director Malcolm Brinded has said he was "shocked and disappointed" that the company had once again overestimated its oil reserves.
Malcolm Brinded has a big job on his hands to turn around Shell
Mr Brinded was speaking after the Anglo Dutch group was forced to downgrade its reserves for the second time in three months and delay its annual report.
The latest downgrade saw Shell slice 220 million barrels from reserves for 2003, and 250 million from 2002.
It follows January's admission that 2003 stocks were 20% over-booked.
That revelation - equal to 3.9 billion barrels - cost its former two top executives their jobs - chairman Sir Philip Watts and vice-chairman Walter van de Vijver.
Mr Brinded replaced Mr van de Vijver.
Thursday's reserves admission saw Shell's share price drop 11p, or 3%, to 361p. But on Friday the shares edged up 0.75p to close at 361.75p.
The matter is doubling embarrassing for Shell because the second downgrading includes reserves from the Norwegian oil field Ormen Lange which it said were still bookable after the January revelation.
"We were working on finalising the 2003 reserves data over the last couple of weeks," said Mr Brinded.
"Concerns arose about the volume of proved reserves bookings proposed for the Ormen Lange field in Norway.
"Clearly it shouldn't have happened, particularly given the attention that this field had already received.
"Obviously as the new chief executive officer I was shocked and I was disappointed by this. The priority clearly is to get this absolutely right."
The publication of Shell's annual report has now been delayed until May so it can sort out the figures.
Its annual general meeting is also being postponed - from April to June.
Shell is also facing an investigation by the Dutch Autoriteit Financiele Markten financial regulatory body for potential insider trading, and another from the US Securities and Exchange Commission.