Energy-related exchange-traded funds were among the top performers Monday, as the threat of a strike in Nigeria had oil and gas futures moving higher.

The front-month crude contract was up 56 cents to $68.56 a barrel, and gasoline was adding less than a penny at $2.26 a gallon.

The iPath S&P Crude Oil Index ( OIL) was higher by 31 cents, or 0.7%, to $38.20. The United States Oil ( USO) added 52 cents, or 0.7%, to $52.05. The PowerShares Dynamic Energy Exploration ( PXE) was rising 27 cents, or 0.9%, to $24.17. The SPDR S&P Oil & Gas Exploration & Production ( XOP) ETF was adding 37 cents, or 0.8%, to $48.98.

The B2B Internet HOLDRs ( BHH) also was on the rise. Holding Checkfree ( CKFR) added 2%, and the ETF was recently higher by 2 cents, or 0.9%, to $2.38.

On the losing side, several biotech-related bundled securities were pressured by a 45% drop in shares of Encysive Pharmaceuticals ( ENCY). On Friday, the Food and Drug Administration refused to approve the company's treatment for pulmonary arterial hypertension, Thelin.

The SPDR S&P Biotech ( XBI) was lower by 71 cents, or 1.5%, to $52.69. The PowerShares Dynamic Biotech & Genome ( PBE) ETF was down 20 cents, or 1.2%, to $18.84. The iShares Nasdaq Biotechnology ( IBB) was recently losing 57 cents, or 0.9%, to $80.72.

Utility-related ETFs were also among the losers of the session. Among individual names, American Electric Power ( AEP), Entergy ( ETR) and Exelon ( EXC) fell by 1% or more.

The Ultra Utilities ProShares ( UPW) was falling by $1.32, or 1.5%, to $84.50. The Utility HOLDRs ( UTH) was off 79 cents, or 0.7%, to $144.61. The Vanguard Utilities ETF ( VPU) eased 44 cents, or 0.7%, to $84.89.