Activist investor Elliott Investment Management has built a stake in oil major BP, a source familiar with the matter told Reuters, Report informs.

The source did not provide the size of the stake.

US-based Elliott is seeking to boost shareholder value by urging BP to consider transformative measures, Bloomberg News reported earlier on Saturday, calling Elliott’s stake in the company “significant.”

The activist investor sees BP as undervalued, Bloomberg reported. BP has a market capitalization of about 69 billion pounds ($85.62 billion), less than half of rival Shell’s value of about 161 billion pounds, according to LSEG data.