Exxon Mobil Corp has hired veteran crude traders Mitch Rubinstein and Michael Paradise in Houston, as the oil major further boosts its trading capabilities, sources familiar with the matter told Reuters on Wednesday.

Exxon has been building a global cadre of experienced traders and beefing up risk management systems to lift profit, in a break from its past.

Previously, Exxon stood apart from rivals by limiting trading activity out of concerns it would be accused of market manipulation. Exxon is valued at about $335 billion, making it the largest U.S. oil company by market capitalization.

Both Rubinstein and Paradise left commodity trader Noble Group Ltd in 2017.

Rubinstein was managing director and global head of crude oil at Noble until 2017, when rival Vitol SA agreed to buy Noble Americas Corp. Noble was once Asia's biggest commodity trader, and has restructured after facing insolvency last year.

Before Noble, Paradise was Citigroup Inc's director of oil trading in Houston.

A spokeswoman for Exxon declined to comment.

Rubinstein updated his LinkedIn profile to reflect his move to Exxon, but his exact title is not clear. A source familiar with the matter said he has already started at the firm.

Both Rubinstein and Paradise will be based in Houston, according to LinkedIn and a source.

Last year, Exxon hired former BHP Billiton Plc trader Nelson Lee as an international crude trader.

This week, Exxon said its oil and gas reserves rose nearly 23 percent last year, driven mainly by increases from holdings in U.S. shale, offshore Guyana and Brazil.