LONDON -- Oil and gas prices have ended the week largely unchanged. Mid-week falls were reversed by comments from European Central Bank President Mario Draghi promising the ECB would do everything possible to save the euro. The United States Oil Fund (NYSE: USO) was up by 1.5% in morning trading on Friday, while the United States Natural Gas Fund (NYSE: UNG) was 0.2% lower than a week ago.

However, stable oil and gas prices weren't enough to protect some small oil and gas companies, whose share prices plunged dramatically during the week. Here are the three of the worst performers:

Range Resources
Range Resources plunged 23% to 5.1 pence this week, thanks to two disappointing drilling updates. Monday's news that the Shabeel North well in Puntland, Somalia, had only found water was not good, while a second update from the same well on Friday delivered more bad news. It left the company's share price hammered and investors hoping that Range will have better luck after the well is deepened beyond its original target depth.

Gulf Keystone Petroleum (LSE: GKP.L)
Gulf Keystone Petroleum lost 15% to 195 pence this week, as investors continue to vacillate over the political and economic prospects of this highly successful Kurdistan explorer. Meanwhile, drilling started this week on the Gulak-1 exploration well, in which Gulf Keystone has a 20% interest. The new well is close to the Bijell-1 discovery well, which has a mean oil-in-place estimate of 2.4 billion barrels of oil.

Borders & Southern Petroleum
Borders & Southern Petroleum continued its descent this week, falling by 15% to 16.5 pence on continued negative sentiment and investor fear over its failure to find oil. Although there was no news from the Falklands region this week, investors continue to be wary about the wider geological and economic challenges faced by the Falklands explorers.

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