In this week's edition of The Motley Fool's energy-focused show, "Digging for Value", analysts Joel South and Taylor Muckerman discuss second-quarter earnings from National Oilwell Varco (NOV -1.06%). With phenomenal top-line growth, the market discounted this valuable supplier due to compressed margins throughout its product portfolio. Check out the video below to hear whether the contracting margins are reasons for concern or present another buying opportunity?