Oil and gas stocks were firmly in the red on Monday as project delays from natural gas giant BG Group and falling crude prices dampened sentiment across the sector.BG, the 13th largest listed company in the UK by market capitalisation, slumped today after scaling back its production guidance for next year by 30,000 barrels of oil equivalents per day (boed) due to delays on the back of the ongoing political and social instability in Egypt and slow progress at its Knarr project in Norway.Meanwhile, it said it would operate fewer rigs in the US due to low natural gas prices, leading to a further 17,000boed negative impact on 2014 volumes.Analysts at Investec said they expected to cut their forecasts for the company by 3-4% on the back of today's update. They said: "Despite strong earnings and cash flow growth, on our current forecasts BG is still trading on a 25% price-to-earnings premium versus the European sector in 2017E."Shares were down 5.62% at 1,210p before the close, its lowest level in two weeks.Oil majors Royal Dutch Shell and BP were also trading in the red this afternoon, along with smaller peers Tullow Oil and Afren.Also weighing on stocks today was a fall in crude with West Texas Intermediate prices pulling back from hitting a two-year high on Friday as the prospect of a potential US military strike on Syria remains up in the air.Furthermore, some reports were citing Lybian officials as having said that oil production from the country had recovered to 600,000 barrels of oil a day.West Texas crude futures for October delivery were down 0.62% at $109.84 a barrel by 16:30 in London, while Brent futures were down 1.12% at $114.82 a barrel.Top performing sectors so far todayTechnology Hardware & Equipment 1,090.48 +2.26%Personal Goods 26,214.22 +1.80%Industrial Metals & Mining 1,563.41 +1.31%Life Insurance 6,155.95 +1.30%Construction & Materials 4,050.09 +0.93%Bottom performing sectors so far todayOil & Gas Producers 7,764.82 -1.44%Food Producers & Processors 6,741.75 -1.15%Industrial Transportation 3,169.97 -0.59%Beverages 14,412.29 -0.53%Electronic & Electrical Equipment 4,177.99 -0.51%BC