Markets were flat yesterday, yet Phillips 66, Valero Energy Corp, Nektar Therapeutics showed impressive gains and made this list of top gainers.

Markets completed a mixed session yesterday while Nasdaq lost 1.07% and ended the session at 12,000. S&P 500 shed 0.25% and closed at 4,090.38.

This limbo state is reflected by published market data as United States Crude Oil Inventories released earlier showed a marked improvement to -3.74 million from the preceding data of -7.49 million, but fell short of the -2.33 million figure forecast by a consensus of market analysts.

Despite yesterday's flat session, several stocks are managing to post notable gains. Take a look at the market's Top Gainers:

+5.48%: Marathon Petroleum ended yesterday at $132.71, a 5.48% increase

After finishing Tuesday at $125.82, the petroleum specialist went up by 5.48% yesterday and remained at the $132.71 level. Currently, the petroleum specialist has a market capitalization of $58.61 billion with an average daily volume of 4.76 million shares. So far this year, it has performed better than the S&P by 14.46%.

+6%: Valero ended yesterday at $135.09, a 6% increase

The energy company closed Tuesday at $127.43. yesterday, it gained 6% and remained around $135.09. The company's market cap currently stands at $49.69 billion with an average daily volume of 5.69 million shares. So far this year, it has been beating the S&P by 6.9%.

Phillips 66 | Closed +6.26% at $104.43

The petroleum refineries company traded at $104.43 yesterday, after making its biggest single-day jump of $6.15 (6.26%) since Feb 10. Having set a significant low of $74.16 6 months ago, the petroleum refineries company is trading 32.52% higher. So far this year, it has been under-performing the S&P by 2.91%. The US energy company's market cap currently stands at $48.13 billion with an average daily trading volume of 4.67 million shares. Phillips 66 expected revenue of $38.96 billion with an EPS of $4.35.

+5.64%: Nektar Therapeutics is up to 75.6 cents (+4.09%) in pre-market trading after closing yesterday's session at 72.63 cents

Bullish sentiment helped the US biopharmaceutical company to hammer out a noteworthy 68.7 cents to 76.85 cents range yesterday, and finally closing at 72.63 cents to end the session. Currently, the polymer conjugate technology developer has a market capitalization of $137.44 million with an average daily volume of 8.53 million shares.