The two biggest supermarket chains - ParknShop and Wellcome - will review their plastic bag rebate programmes after criticism they did not reduce the numbers used.
A quarter of the bags given away were superfluous, a survey by the Green Student Council found.
The two chains said they would examine the rebate schemes to decide if more promotions were needed.
'We will review the present programme and if we find the customers do not know the programme very well, more promotions will be done,' a Wellcome spokeswoman said. ParknShop said it would do the same.
Wellcome gives a 10 cent rebate - to a maximum of $1 per transaction - to customers for every bag they save on purchases over $25. ParknShop offers the same deal, but customers can save up to $2 per transaction.
While saying education and environmental awareness were the responsibility of the government, both ParknShop and Wellcome insisted their plastic bags made up only 2 to 3 per cent of the plastic bags found in landfills.