LONDON -- Oil and gas prices held firm this week, with Brent Crude finishing the week above $101 and WTI heading toward the $87 level. The rises were largely due to a tightening of U.S. sanctions on Iran that drastically reduce the amount of oil the Middle Eastern producer can export to world markets. The latest growth figures from China also reassured investors, as quarterly growth was on target at 7.6% over the year-ago period, dampening fears that growth would fall below forecasts.

In the ETF market, the United States Oil Fund (NYSE: USO) was up by around 2.2%, while the United States Natural Gas Fund (NYSE: UNG) was down by 2.7% when U.S. markets opened on Friday, despite a small rise in natural-gas prices during the week.

Despite only modest gains in oil and gas prices, some junior oil and gas shares managed to outperform the market by a big margin. Here are three of this week's top climbers.

Lansdowne Oil & Gas
Lansdowne Oil & Gas (LSE: LOGP.L) climbed by a further 15% this week, making it into our top three for a second consecutive week. The Celtic Sea explorer's share price is now up by 62% on the month in anticipation of good news regarding funding and a strong Barryroe resources update, both expected at the end of July.

Chariot Oil & Gas 
Chariot Oil & Gas (LSE: CHAR.L) rose by 9.2% this week on solid volumes, although it peaked even higher during the middle of the week. There were no new developments this week, but Chariot is due to start drilling a new exploration well shortly at its Nimrod prospect in offshore Namibia.

Xcite Energy
Xcite Energy (LSE: XEL.L) rose by 8.3% this week after it gave markets a positive update on the preproduction flow test being performed on its Bentley well. Xcite's shares have fallen heavily recently, as the North Sea explorer has been forced to raise new funds to continue with its development of Bentley. Even after this week's increase, its share price remains 15% down on the month.

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