very interesting query- please help

Ost Ocity Dstate Dcity Carrier Price Rank Diff
A B C D X 1200 1 100
A B C D Y 1300 2 100
A B C D Z 1350 3 100
A B C D W 1789 4 100
A1 B1 C1 D1 X1 785 1
A1 B1 C1 D1 Y1 789 2
The rank for every carrier is based on the price . If rank1
carrier
is not a pariticular carrier(say if it is not X1 or
Y1 or Z1), then i want to calculate the difference between Price
corresponding to rank1 and price corresponding to rank2. and fill the
Diff column with the value. I want a query which can create that
difference coln ( last col) as in the above example. The first four
rows is one lane and the last two rows is another lane. For the
second
set of lane, the diff col will be empty because tthe carrier is X1.
Can somebody please help me in writing this query.

Thanks in advance