REGULAR OFFSET SPACING vs. REGULAR TRACE SPACING
The following is an example of setting the offset increment (parameter incoffo=) to -99. When you do this it creates output offset bins such that the number of input traces in each offset are equal. Normally you make the offset increments equal(i.e. 1000, 2000, 3000, etc). However, this can result in a very different number of input traces going into each offset bin. This option makes varying offset increments such that the number of input traces in each offset are the same.

In each example below, the gather on the left is the traditional way showing low amplitude traces for the near offsets. The gather on the right has them equalized so you can see all the traces in the gather have about the same amplitude.