A formalism for canonical variational theory calculations on atom-diatom reactions with linear generalized transition states is presented. Anharmonicity is included in both stretches and bend. O A set of 36 realistic potential energy surfaces is generated by an extended and modified bond energy-bond order method. The canonical variational formalism is applied using these surfaces and the resulting thermal rate constants are compared to those predicted by conventional transition-state theory for the same reactions. The median ratio of the conventionally calculated rate to the canonical variational one increases from 1.6 at 200 K to 2.0 at 2400 K. The error is generally larger for reactions with symmetric saddle points and for those with very asymmetric saddle points. Ten representative reactions are discussed in detail to illustrate the competition and reinforcement of various factors in determining the location of the generalized transition state and the effect of varying this location.