Abstract: The sizing agents are mixtures of alkenyl succinic anhydrides in which the alkenyl groups have in the range of about 6 to about 40 carbon atoms, and in which at least 97 wt % of the alkenyl groups are bifurcated on the alpha carbon atom into two branches neither of which has less than two carbon atoms. Other characteristics of the mixture are that (1) 20-50% of the bifurcated alkenyl groups have only one methyl or methylene substituent and no other side chain, and the remainder of such bifurcated groups have two straight chain branches (no side chain) emanating from the alpha carbon atom, (2) at least 3 alkenyl succinic anhydrides that differ in the number of alkenyl carbon atoms are each present in at least 5 wt % in the mixture, (3) no more than about 50 wt % of the alkenyl succinic anhydrides is any given alkenyl succinic anhydride or mixture of isomers having the same number of carbon atoms in their alkenyl groups, (4) the average number of carbon atoms in the alkenyl groups is ca.