Benzinga's Volume Gainers

A number of notable stocks are moving higher on Monday on very heavy volume despite a broader market which is marginally lower on the session. Among the names that traders may want to keep an eye on are PetMed Express

, BroadVision

, Zillow

, Stamps.com

, and Carrizo Oil & Gas

. Below, Benzinga examines what is driving the unusual activity in these stocks.

- Prior to the opening bell, PETS released better than expected quarterly earnings results. The company reported adjusted EPS of $0.19 versus Wall Street analysts' consensus estimates of $0.16. Revenues were up 12% year over year. PETS shares have surged 12.69% to $12.70 in the wake of the bullish report. Volume is running at 879% above average.

- This small-cap stock is on fire! Over the last month alone, BVSN shares are up more than 200%. On Monday, the stock has added another 19.44% to $32.25. Volume is running at 726% above average. At this point, the move in BVSN, which only has a market cap of $143 million, is likely being driven by pure momentum and could reverse shortly. In fact, today's large volume spike may be signifying a blow-off top in the stock.

- Zillow shares have added 2% to $28.40 on Monday. Volume has been heavy with around 300,000 Z shares trading hands compared to a 3-month daily average of 135,000. The does not appear to be any obvious news driving the activity in the stock.

- Shares are up 2.51% to $31.02 on heavy volume on Monday. The company issued a press release this morning touting that its online postage and shipping software has automatically been upgraded to accommodate new USPS postage rates that went into effect today. Volume is running at 92% above average.

- Carrizo has added 6.32% to $24.55 during Monday's trading session. The move in the stock coincides with a rally in the energy sector after Apache

acquired Cordillera Energy Partners. Volume in CRZO is running at 50% above average.