STOCKS to watch on the Australian stock exchange on Tuesday April 30 The share price of minerals explorer Aquila Resources took a hammering after its Japanese joint venture partner pulled out of some of its Queensland coal exploration permits. BHP - BHP BILLITON - down four cents at $32.54 STO - SANTOS LTD - down three cents at $12.24 Oil and gas producer Santos has committed to a $100 million drilling and appraisal program over the next 12 months in the Northern Territory. Queensland government has approved the state's first Costco store, overriding rival Westfield's attempt to lock out a competitor.