LONDON -- This week saw the FTSE 100 and most other European stock markets hit by volatile sentiment and a lack of concrete action over the eurozone crisis. Fortunately, the oil price held firm, with Brent Crude remaining in the $103 to $105 range all week. U.S. benchmark WTI crude behaved similarly and spent the week moving between $87 and $90 per barrel.

As a result, the United States Oil Fund (NYSE: USO) was down just 0.03% on the week when U.S. markets opened on Friday morning.

Gas prices proved less robust, and ongoing supply surpluses, along with BHP Billiton's substantial writedowns on its shale gas assets, sent the price of gas below $3 per MMBtu once more this week, leaving the United States Natural Gas Fund (NYSE: UNG) trading 8% lower on Friday morning than at the start of the week.

A stable oil price isn't always enough to protect the share prices of small oil and gas companies, whose fortunes depend heavily on their luck at the drill bit and speculative trading. Here are three of this week's worst performers -- including one surprisingly big name.

Ophir Energy (LSE: OPHR.L)
Ophir Energy
fell 13% to 520 pence this week in what many analysts believe is a rather harsh judgment on its latest drilling result, which found 500 billion to 2 trillion cubic feet of gas -- a solid success! The only problem was that traders have come to expect Ophir to beat forecasts, whereas this time it didn't. Ophir remains a highly rated company with a lot of solid assets and highly prospective resources. Is it one to consider buying at this price?

Northern Petroleum (LSE: NOP.L)
Northern Petroleum
fell almost 7% to 65 pence this week in choppy trading that appears to have little underlying cause. Somewhat unusually, the company reconvened its recent annual general meeting this week, but this may have been due to a procedural technicality, according to some reports.

Lansdowne Oil & Gas (LSE: LOGP.L)
Lansdowne Oil & Gas
slipped 5.3% this week to 61 pence, with this week's RNS announcements suggesting that one cause might be profit-taking by an institutional shareholder after the company's share price doubled last month. Lansdowne's prize asset is its 20% stake in the Barryroe field in the Irish Sea -- but the company needs funding or a partner to fund its share of further development, and investors are now left to wait and see how this will play out.

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