* Q1 Replacement Cost profit up 135 percent at $5.6 billion
* Underlying result well ahead of forecasts
* Says working to contain Gulf of Mexico oil spill
LONDON, April 26 (Reuters) - Oil major BP Plc (BP.L) said first quarter replacement cost profits jumped 135 percent to $5.65 billion, on the back of a big jump in crude prices.
Excluding one-off items, which amounted to a net charge of $49 million, the result was $5.65 billion ahead of an average forecast of $4.78 billion from a Reuters poll of nine analysts.
The world's third-largest Western oil major by market value said production was broadly flat at 4.01 million barrels of oil equivalent per day.