By Sarah Turner

Shares of oil and gas firms as well as miners weakened in a mildly lower London market Wednesday, with Tullow Oil and Antofagasta under notable pressure after reporting earnings.

In the oil and gas sector, natural-gas producer BG Group declined 1.6% and oil major BP fell 1.1%.

The losses came after light sweet crude futures tumbled in New York trading on Tuesday.

Crude-oil futures were up 10 cents at $72.15 a barrel in electronic trading on Wednesday ahead of weekly U.S. data on petroleum inventories.

Shares of Tullow Oil declined 3.9%, in the process paring gains made this quarter to 12.3%.

Earlier Wednesday, the company said that first-half net profit fell 83% to 21.4 million pounds and that sales dropped 23% to 291.3 million pounds, reflecting a 16% decrease in production.

Miners were also retreating from recent gains, with shares of Rio Tinto (RTP) trading down 2.4% and Antofagasta skidding 4.7%.

The latter's first-half net profit fell 70.3% to $235.7 million as revenue dropped 51% to $1.2 billion, reflecting lower commodity prices and lower copper production.

Overall, the FTSE 100 index declined 0.6%, pulling back by 27.15 points to stand at 4,889.65. Other European shares were also lower, as were U.S. stock futures.

Also on the move in London, shares of advertising giant WPP (WPPGY) fell 3.4% after first-half-attributable profit fell 47.9% to 108.4 million pounds.

WPP said the lower results reflected the impact of a significant global economic contraction on most regions and service sectors. "The impact continued to intensify in the second quarter, though results for July did indicate a 'less-worse' picture," the company said.

On the positive side, shares of brewing giant SABMiller rose 1.3%. Peer Heineken reported a forecast-beating 20% rise in profit on Wednesday.

Also, shares of Serco Group rallied 5.4%. First-half net profit rose 33.8% to 61.4 million pounds as revenue climbed 30.8% to 1.9 billion pounds.

Serco said that it saw increasing levels of activity in its markets and that the second half of the year has started well, putting the company on track to deliver on its 2009 forecast. Order book stood at 16.7 billion pounds at the end of June, up from 16.3 billion pounds recorded at the end of 2008.