The Senate inquiry into supermarket pricing has threatened Woolworths boss Brad Banducci with contempt for failing to answer simple questions.

Mr Banducci was warned he could face six months in prison or a $5,000 fine if he was held in contempt by the Senate committee.

The Woolworths chief executive was appearing before senators in Canberra to answer questions about the supermarket giant's pricing behaviour.

But things went awry when Greens senator Nick McKim, committee chair, asked Mr Banducci if "return on equity" was an important measure of corporate profitability.

Mr Banducci refused to answer the question, and he repeatedly refused to answer it despite the question being asked over a dozen times.

The back and forth between Senator McKim and Mr Banducci became so repetitive that Mr Banducci was warned that the committee could hold him in contempt.

"I'm not interested in your spin or your bullshit," Senator McKim said.

And after Mr Banducci continued to refuse to answer the question, Senator McKim suspended the committee to discuss the issue of contempt with his committee colleagues.

When proceedings returned and the inquiry picked up again, Mr Banducci was given one final warning about answering simple questions.

With the threat of contempt in the air, Mr Banducci told senators that if it helped to push the hearing forward, he would be happy to say he didn't know what the return on equity was for Woolworths Group last financial year.