By Carla Mozee, MarketWatch

Plunge in oil prices weighs on energy sector

U.K. stocks slipped Tuesday, with energy shares losing ground after oil prices sank to their lowest settlement in three months.

The FTSE 100 fell 9 points, or 0.2%, to 6,526.04. The benchmark has declined over the past two sessions.

The energy group was the worst performing in the wake of Monday's 7.7% slide in (http://www.marketwatch.com/story/crude-oil-struggles-to-recover-from-selloff-2015-07-07) oil prices , and which also saw a 6.3% drop for Brent crude . Turmoil in Greece and concerns about a potential flood of Iranian oil into the global market are seen by analysts as among the reasons for the price declines.

Shares of British oil major BP PLC (BP.LN) (BP.LN) fell 1.5%, Royal Dutch Shell Group PLC (RDSB.LN) (RDSB.LN) lost 0.7% and BG Group PLC (BG.LN) gave up 0.7%. Weir Group PLC (WEIR.LN) was 2.6% lower. The energy-engineering firm said it plans to purchase Delta Industrial Valves Inc. for an enterprise value of up to $47 million.

In other oil-market news, French oil-services firm Technip SA (TEC.FR) late Monday issued a profit warning (http://www.marketwatch.com/story/technip-shares-down-8-after-cost-cutting-program-2015-07-07) and said it's cutting down the size of its global workforce by 6,000 as it "anticipates an even more challenging environment in the oil and gas" industry.

But moving higher on the FTSE 100 were shares of Marks & Spencer Group PLC (MKS.LN). The apparel and food retailer said its full-year outlook remains unchanged (http://www.marketwatch.com/story/marks-spencer-sales-rise-stands-pat-on-forecast-2015-07-07) as it reported a 1.8% rise in group sales for the 13 weeks ended June 27.

Also higher was Lloyds Banking Group PLC (LLOY.LN), up 0.8% after a ratings upgrade to hold from sell at Investec. After "a modest pullback in the share price, we now see the stock at close to fair value," said Investec.

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