"XTO’s resource base is the equivalent of 45 trillion cubic feet of gas and includes shale gas, tight gas, coal bed methane and shale oil."That's about $0.91/MMBTU of XTO gas resources. Compare that to Alaska's gas estimated at 169 trillion cubic feet. Figure half of that is on Exxon leases. Figure $30 billion for a pipeline, $15 billion for Exxon's share - that works out to less $/MMBTU for gas resources in Alaska.
Apparently the cost of bringing XTO resources to market is more attractive to Exxon than Alaska gas....today. But stay tuned.