** Australia's energy index rises as much as 1 pct** Oil prices extended gains on Monday as U.S. sanctions against Iran pointed towards a tighter market
** Brent crude oil futures were at $72.88 per barrel at 0053 GMT, up by 7 cents from last close when it had risen more than 1 pct
** Australian oil companies Beach Energy Ltd, Oil Search Ltd and Woodside Petroleum Ltd post gains in the range of 1.1 pct and 2.3 pct
** Woodside posts steepest intraday pct gain in more than 1 week
** Santos Ltd climbs 1.5 pct; says fourth gas rig started operations at Cooper Basin site in South Australia, as it looks to ramp up output to supply markets in the east of country