le="Agip">Agip</a>/<a href="//en.wikipedia.org/wiki/Eni" title="Eni">Eni</a>, <a href="//en.wikipedia.org/wiki/Total_S.A." title="Total S.A.">Total</a>, <a href="//en.wikipedia.org/wiki/Marathon_Oil" title="Marathon Oil">Marathon Oil</a>, <a href="//en.wikipedia.org/wiki/Veba" title="Veba" class="mw-redirect">Veba</a> and Verenex Energy. Challenger works as a regular subcontractor to the state-owned <a href="//en.wikipedia.org/wiki/National_Oil_Corporation" title="National Oil Corporation">National Oil Corp