The Transport Minister has backed commuters who manipulate their travel to get the best deal out of their Opal card, potentially saving them, and costing the government, hundreds of dollars a year.

Under the Opal fare structure, travel is free after the card-holder has made eight trips in a week.

Rowan Barker on his afternoon ferry. Credit:James Alcock

This has created an incentive for people to take cheap - and potentially useless - trips early in the week to make significant savings later on.

"I want people to beat the system," Gladys Berejiklian said. "I want people to find the savings because they are there to be had," she said.