LNG-
Wewll, as you know it's about 90-100% Methane, so it's density is 26.5 LBs/Ft3... and weight about 3.5 lbs/gallon. the Boiling temp is -259F and molecular weight is 16.04 Energy content is about 83,000BTU/gal and LFL=5% and HFL=15%. The Viscosity can vary, but burning(flame) velocity is about .98 ft/sec.
Hope this helps... I imagine there are alot of sites out there you could try SPE (Society of Petroleum Engineers) though.