Daily oil production at the Azeri-Chirag-Guneshli (ACG) oilfields, which account for most of Azerbaijan's output, declined to an average 651,000 barrels per day (bpd) from 661,000 bpd a year ago.
BP said in its report it spent around $137 million in operating expenditure and $396 million in capital expenditure on ACG in the first three months of this year.
Azerbaijan said its total crude oil and condensate production fell to 13.98 million tonnes in the first four months of 2016 from 14.23 million a year earlier.
Natural gas output from the Shah Deniz offshore field in Azerbaijan rose to 2.7 billion cubic metres (bcm) in the first quarter of this year from 2.6 bcm in the same period of 2015.
It produced 0.6 million tonnes of condensate, the same as in the first quarter of the last year.
BP said the Shah Deniz consortium spent around $116 million in operating expenditure and about $928 million in capital expenditure on the project in the first quarter of this year.
Shah Deniz is estimated to contain 1.2-1.5 trillion cubic metres of gas.
Shah Deniz I has been pumping gas since 2006, while gas from its second stage is expected to reach Europe by 2019-2020.
Overall gas production in Azerbaijan fell to 9.847 bcm in January-April from 9.898 bcm a year earlier due to a decline in production by Azeri state energy company SOCAR.
Azerbaijan plans to produce 41 million tonnes of oil and 29 bcm of gas in 2016.