NDP Critic Buckley Belanger said there is a lack of transparency on where the money is going.
"What does it cost to build a kilometre of highway today?" he said. "And how is it a cost (goes) up so much?"
In 2008-09, the ministry spent $12.1 million on consultants compared to $61.3 million in 2013-14.
Belanger said the NDP wants a breakdown of where the money is being spent and how many kilometres of roads are being built.
"We've been using consultants all the time ... exactly how much more are they costing us?" he said.
Nancy Heppner, minister of highways and infrastructure, said the increase corresponds to the number of projects.
"And we're doing big projects, interchanges, passing lanes, twinning of highways," she said. "We're doing far more work."
She added that use of in-house experts isn't declining and more specialists overall are needed.
"I'm satisfied that the resources within the ministry are being used well," she said.