Is there a table that shows how 8b/10b encoding tries to ensure running disparity on a transmission line?
Basically what's done is some 8-bit message words have two corresponding 10-bit code words. One of these has positive disparity (more 1's than 0's) and the other has negative disparity (more 0's than 1's). 

When encoding you keep track of the running disparity. If the running disparity is positive and the next input octet gives you a choice of code words, you pick the one with negative disparity, and vice versa.