Core earnings fell 41% to $1.59bn (Â£1.03bn), with pre-tax profits down to $708m from $1.9bn a year earlier.
Like many other energy companies, BG's results have been affected by the fall in oil prices from a year ago.
BG said it was still happy with Shell's Â£47bn offer for the firm, despite a recent recovery in oil prices.
"There is no change to our view on the offer," said BG chief executive Helge Lund.
BG agreed to be bought by Royal Dutch Shell last month. Mr Lund said the deal was expected to be completed by early-2016.
BG more than doubled production from its Brazil and Australia operations in the first quarter.
However, the impact of the lower oil price from a year earlier was seen in a 21% fall in revenues to $3.99bn.
UK oil and gas exploration firm BG Group, which is set to be taken over by Royal Dutch Shell, has reported a big drop in first-quarter earnings.