HANG Seng Index futures had a positive day yesterday, with the August contract rising 130 points, to 9,380, a premium of 43 points over the cash. The September contract rose 136 points to 9,385. Turnover was 25,697 contracts in activity boosted considerably by roll-overs. In the August contract the turnover was 13,609 contracts, and in September it was 12,088. At the open, domestic buying was strong, then overseas money flooded in, adding to the positive sentiment. Confirmed open interest for Wednesday was 17,169 contracts in August and 21,429 in September. In index option trading, bulls bought September 8,800-9,200 put spreads, said Jardine Fleming. Bears sold September 9,200 calls. Front-month implied volatility was up a bit, to 28.5 per cent. Volume in options was at 2,076 lots. The open interest was 46,276 lots. This was split with call and puts in August being 7,707 and 6,542 respectively. In September, they were 13,541 and 13,073 respectively. In December, they were 1,997 and 3,318 respectively. Many investors are betting on a rise in volatility in September and October and are making maximum use of the period of depressed implied volatility to benefit from the expected increase.