Following yesterday's heightened trading volumes, National Oilwell Varco Inc, Tenaris S.A., Pioneer Natural Resources Co were the standout stocks.

A quick recap of where the last trading session ended: Markets had an interesting day yesterday; S&P 500 closed the day at 4,135.35, having gained 1.96%. Dow Jones gained 1.57% and closed at 33,826.

Why Trading Volume Matters

Trading volume is simply the total number of shares traded including both buy and sell orders. If a stock has appreciated on high volume, it is more likely to be a sustained move compared to an appreciation with low volume. Typically, high volume trading sessions are considered significant occurrences and closely watched by traders.

Price action was mostly bullish yesterday with some energy stocks recording abnormally high trading volumes. Here's a recap:

NOV Inc. | 283% above rolling average

National Oilwell Varco Inc went down to $16.56 (8.1%), adding to its four days of losses. The hydrocarbon exploration enabler is now trading 29.08% below its 3-month high of $24.8. The hydrocarbon exploration enabler's market cap currently stands at $6.52 billion with an average daily trading volume of 4.39 million shares.

With 12.42 million shares traded yesterday, NOV beat its daily average by 283% to cap off a frenetic trading day.

Tenaris | 203% higher than rolling average

Tenaris outpaced its average daily trading volume (2.20 million) with 4.47 million shares traded yesterday.

Having set a significant high of $36.67 2 months ago, the steel piping manufacturer is trading 22.31% lower.

Pioneer Natural Resources | 220% higher than rolling average

Pioneer Natural Resources hit a significant low of $181.85 around a month ago, but has since recovered 22.34%. Pioneer Natural Resources is currently trading with a market cap of $49.74 billion with an average daily volume of 2.51 million shares.

Trading volume peaked at 5.52 million shares yesterday, thereby obliterating the daily average of 2.51 million by 220%.

— Average trading volume refers to a 21-day rolling average.