A weekend deal to limit Iran's nuclear activity prompted a sharp fall in oil prices on Monday, sending oil and gas stocks into the red whilst sparking gains in the travel sector.Iran and the so-called P5+1 nations of Russia, China, France, Germany, the UK and the US came to an interim agreement over the weekend limiting Iran's nuclear programme in exchange for the easing of economic sanctions. The deal will run for the next six months as both sides work on a final agreement. Iran is home to the world's fourth-largest oil reserves but its exports have been affected by tough sanctions. The nation will not be allowed to increase its oil sales for six months but the deal has relieved tensions in the oil producing region of the Middle East.Brent crude futures for January delivery were down 1.18% at $109.74 a barrel before the close of trade, after having dropped 3% earlier on in the session."The deal is a major step forward in the negotiations on Iran's nuclear programme following a decade of struggles," said analyst Jens Nærvig Pederson from Dankse Bank."As Iran is not allowed to increase its oil exports, the effect [on oil prices today] probably reflects relief in the market that the sides are finally moving closer together and an expectation that the momentum will continue to grow."BP, Shell, Tullow and BG Group were all trading in the red before the close, tracking crude lower.BP was also lower after the US judge overseeing the entire civil liability trial arising from the Gulf of Mexico oil spill criticised the company's "deeply disappointing" attempt to block what it sees as excessive compensation payments.In contrast, travel stocks such as easyJet, IAG, Carnival, TUI Travel and Thomas Cook were making gains as the price of oil fell."News that the US has struck a deal with Iran on its nuclear activities has seen both WTI and Brent oil prices decline, and has to a degree lessened the risk premium normally associated with Middle-East tensions," said Brenda Kelly, Senior Market Strategist from IG.Meanwhile, Jefferies raised its rating for easyJet from 'hold' to 'buy', saying that after a pause for breath over the summer "we are now increasingly confident of a return to share-price outperformance". The broker also lifted its target price for the stock, along with IAG.Top performing sectors so far todayTravel & Leisure 6,918.08 +1.63%Financial Services 7,508.08 +1.47%Electronic & Electrical Equipment 4,198.35 +1.46%General Industrials 4,255.29 +1.32%Personal Goods 24,031.06 +1.29%Bottom performing sectors so far todayMining 16,139.69 -0.66%Oil & Gas Producers 8,091.02 -0.40%Fixed Line Telecommunications 4,320.35 -0.31%Pharmaceuticals & Biotechnology 11,636.82 -0.06%BC