Oil rose on Tuesday after one of its biggest sell-offs this year but looked vulnerable to more falls after China’s stock market took another tumble and Greece moved closer to leaving the euro zone. Brent crude for August was up 70 cents at $57.24 a barrel by 0920 GMT (10:20 a.m. BST), following a more than 6 percent drop in the previous session. “After yesterday’s sharp and fierce sell-off it is impossible to paint an even remotely bullish technical picture,” said Tamas Varga, analyst at brokerage PVM Oil Associates.