LONDON -- Oil prices remained firm last week as neither Hurricane Isaac nor the refinery fire in Venezuela managed to cause any serious disruption to supplies. Operations in both areas are expected to get back to normal this week, relieving any possible pressure on supplies.

Despite this, the price of crude oil has stayed high. Shortly after London markets closed on Monday, Brent crude for October delivery was trading at $115.50 per barrel, while WTI crude was $96.70. U.S. markets were closed for the Labor Day holiday on Monday, but on Friday the United States Oil Fund (NYSE: USO) closed up by 1.4% on the week, while the United States Natural Gas Fund (NYSE: UNG) was up 1.7% on the week.

Oil prices have been strong all summer, but some small oil shares have outperformed the market by a big margin. Here are three of the summer's top climbers:

Quadrise Fuels International (LSE: QFI.L) has soared 118% to 10.4 pence over the last 30 days, after it gained heavyweight backing from Saudi group Rafid for trials of its synthetic heavy fuel oil with utility and refinery companies in Saudi Arabia. Although not technically an oil company, QFI has outperformed its peers in the oil and gas producers sector thanks to the deal. QFI's share price was given an extra boost by news that container shipping company Maersk has opted to extend its seagoing trials of the fuel.

Amerisur Resources (LSE: AMER.L) is up by 80% to 37 pence over the last three months. Amerisur is focused on Colombia and has delivered a string of solid progress reports and good news to the market over the last few months, as several of its Platanillo wells have been successfully completed and placed on production.

Xcite Energy (LSE: XEL.L) has climbed 48% to 113 pence over the last month, after its Bentley field in the North Sea was finally been brought into production. Xcite also seems to have got to grips with its recurring funding problems, albeit at the cost of some dilution to shareholders.

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