Keith Shoemaker, managing director of North American natural gas trading, and William Hartz, head of financial oil trading, have resigned, BNP Paribas' head of commodity derivatives Catherine Flax told Reuters.

She did not give a reason for their departures.

Shoemaker, who had been with BNP Paribas for six years, is a veteran energy trader who has held senior positions at J.P. Morgan, Sempra Energy, Phibro, Louis Dreyfus and Mobil, among others, according to his LinkedIn page.

Hartz joined BNP Paribas in 2005 from Bank of America, where he managed the petroleum trading book, according to a profile of him by Risk.Net magazine.

Energy news website Sparkspread was the first to report on Monday that the two had quit.

The report also cited the August resignation of Dora Sung, BNP Paribas' head of commodities trading for the Americas, and the earlier departures of two other senior commodity team members, including Marc Fontaine, former head of commodity derivatives.

BNP Paribas' Flax said the report gave the impression that the bank was downsizing its commodities and energy desk in New York, but noted "that's not the case at all".

"For sure, we're expanding and we're in a growth mode. There are a number of ways to expand the business and that includes adding clients and adding personnel," she said, without elaborating.

A source at BNP Paribas said Sung retired after more than a two-decade career at the bank. Fontaine's LinkedIn page said he quit in 2013.

(Reporting by Barani Krishnan; Editing by Dan Grebler)