Royal Dutch Shell saw its listings fall 3.1 percent and 2.8 percent respectively after it warned that its fourth-quarter figures are expected to be significantly lower than recent levels of profitability because of oil and gas prices and problems with its refining business.
"It's not good. When you're talking about higher costs and lower production volumes, it's a lethal combination," Nick Xanders, who heads up European equity strategy at BTIG, said.
"It's symptomatic of the entire market, with costs rising but revenues not coming through. Some hope that it's a company specific thing, but I don't think it is."
At its peak fall, the drop knocked around 6.5 billion pounds off Shell's market capitalisation, while the broader energy sector wiped 26 points off the FTSE 100, enough to erase any gains on the market.
The index was flat at 6,818.05, despite the fact that four in five stocks were in positive territory. It underperformed euro zone peers, with the euro zone blue-chip EuroSTOXX 50 up 0.2 percent.
Miners extended a bounce after Rio Tinto's good results on Thursday to trade 7 percent higher so far this week.
The FTSE 100 is up 1.2 percent since Monday, set for its biggest weekly gain of the year, after a strong rise on Wednesday lifted the index out of a tight 100 point trading range that had prevailed since the start of 2014.
The gains have taken the index to within a point of October's high at 6,819, 0.8 percent off 2013's high and 2 percent off an all time high set 14 years ago.
"Wednesday's gains were held onto yesterday and we continue to sit just below (the October high)," Clive Lambert, analyst at FuturesTech, said in a note.
"Taking out last year's highs and gunning for the late 1999 all-time high must be in bulls' thoughts now."