No, methane is lighter than air. (See various talk entries below.) The linked MSDS has moved, try this one: (http://avogadro.chem.iastate.edu/MSDS/methane.pdf) Toward the end you'll find Section 9: Physical and Chemical Properties. Note the SPECIFIC GRAVITY (Air = 1): 0.554. This means it is about half as heavy as air, and will not pool to form concentrations as heavier-than-air vapors might.