Oil and gas producers ConocoPhillips, ENI and BG Group reported big jumps in second quarter profits on Wednesday thanks to higher oil and gas prices and firmer refining margins.

Conoco, the third-largest U.S. oil company, said second quarter net profits rose 385 percent to $4.2 billion, boosted by a $2.9 billion gain related to the company's sale of its stake in a Canadian oil sands venture.

However, underlying or adjusted profits rose 150 percent -- likely to be one of the highest gains in the industry as a turnaround in refining helped the company, which has one of the heaviest refining weightings of all the integrated oil majors.

Earnings per share exceeded analysts' forecasts.

Italy's Eni said its second quarter adjusted profit, comparable to Conoco's measure as it excludes one-offs and non-cash charges ignored under U.S. accounting rules, rose 80.2 percent to 1.63 billion euros ($2.1 billion) and also beat predictions.

Britain's BG Group, whose output is mostly gas and which does not own refineries saw adjusted or underlying profits rise 19 percent to $899 million ahead of an average forecast of $839 million in a Reuters poll of six analysts.

On Tuesday buoyant refining margins also boosted earnings for the U.S. Valero Corp.

BP Plc, which pumped more than any other non-government controlled oil company last year, said on Tuesday that underlying profits rose 77 percent in the quarter, although a $32 billion charge to clean up its oil spill created a big headline loss. Shares in Conoco, which also announced it would sell its entire stake in Russia's Lukoil, rose nearly 2 percent in premarket trading, while shares in Eni traded down 0.26 at 1319 GMT (9:19 a.m. ET), outperforming a 0.5 percent drop in the STOXX Europe 600 Oil and Gas index.

BG shares traded down 2.5 percent.

Conoco said oil and natural gas production fell 8 percent to 1.73 million barrels of oil equivalent per day (boepd), as new finds failed to keep pace with natural field decline.

BG said output fell 2 percent to 623,000 boepd, while Eni said production was flat in the quarter compared to the same period last year at 1.76 million boepd.

Western oil companies face a challenge growing production as countries with the richest resources, including Russia, Venezuela and Saudi Arabia restrict investment in their energy sectors.

U.S. crude prices were 30 percent higher in the quarter to the same period last year, averaging $77.81/barrel, while average global refining margins rose 10 percent, according to figures from BP.

(Reporting by Tom Bergin; Editing by Mike Nesbit)

($1=.7684 euros)