Oil behemoth BP saw profit fall in the first quarter, as costs for the clean-up of the Gulf of Mexico oil spill continued to mount.

The FTSE 100-listed company, which has been dogged by the deepwater drilling disaster that erupted just over a year ago posted profit of $5,481 million, compared to $5,598 million a year earlier.

A pre-tax charge of $400 million dented profits and combined with the $40.9 billion the company has already earmarked to pay for the disaster, takes the total charge over $50 billion. The firm said all charges relating to the incident had been treated as non-operating items.

The impact of the spill could also be seen in BP's net cash provided by operating activities, which was $2.4 billion compared to $7.7 billion in the same period in 2010. This included a $2.8 billion net cash outflow relating to the Gulf of Mexico.

BP said the majority of the shoreline clean-up phase had been completed during the period, in addition to most of the subsea work including the plugging and abandonment of the second relief well. The firm also provided details of local restoration, research and donations it is undertaking to try and make amends for the environmental ruin it inflicted.

Production for the quarter was 3,578 million barrels of oil equivalent per day, 11 per cent lower than the first quarter in 2010. BP said this reduction primarily reflects the impacts to the Gulf of Mexico production as a result of the drilling moratorium, higher maintenance activity in the North Sea and in Angola, and the Trans-Alaska Pipeline System interruption. It added the reduction had been partly offset by first production from Iraq.

Despite this, profit from exploration and production did increase during the first quarter to $8.42 billion, compared to $8.29 billion in the first quarter of 2010. Unsurprisingly, a regional breakdown showed US exploration and production profit fall to $1.87 billion from $2.76 billion, while non-US exploration and production profit increased to $6.54 billion from $5.53 billion a year earlier.

Looking ahead the firm said it expected second-quarter production to 'reflect the continued impact on operations in the Gulf of Mexico' following the drilling moratorium.