By Justin Scheck and Rory Gallivan 

LONDON-- BP PLC on Tuesday reported a fall in first-quarter profit from a year earlier, giving the first glimpse of how low oil prices through the beginning of 2015 affected the world's biggest oil companies.

BP's replacement-cost profit--a number similar to the net income that U.S. oil companies report--was $2.1 billion, down from $3.48 billion a year earlier. Revenue fell to $54.9 billion from $75.1 billion from a year earlier.

Production for the quarter was 8.3% higher than the first quarter of 2014 at 2.31 billion barrels of oil equivalent a day.

"Looking ahead, we expect second-quarter 2015 reported production to be lower than the first quarter, reflecting significant seasonal turnaround and maintenance activity," the company said.

Underlying adjusted replacement cost profit in BP's downstream, or refining, division was up to $2.16 billion from $1.01 billion, but in the upstream division, which finds and produces new oil and gas, it was down to $604 million from $4.4 billion.

BP, like other oil producers, has been hit hard by slumping oil prices since mid-2014.

The weak prices compound BP's already considerable challenges. For the past five years, the company has been trying to recover from its fatal 2010 Deepwater Horizon disaster in the Gulf of Mexico.

On Tuesday the company reported a net pretax charge of $332 million related to the disaster.

BP has sold more than $40 billion in assets to raise cash for cleanup and legal costs related to the Gulf of Mexico spill. While those costs are winding down, BP's ability to spend on new reserves remains limited as it tries to limit spending while oil prices are low.

In contrast, U.K. rival Royal Dutch Shell PLC is using weak prices as an opportunity to invest, with a deal to acquire BG Group PLC for $70 billion.

Write to Justin Scheck at justin.scheck@wsj.com and Rory Gallivan at rory.gallivan@wsj.com

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