If, as Ovidius already said, you have a real problem with chained row you could try to use a larger block size for this table. This is possible by using the mutiple block size feature (which is only available since Oracle9i).
To do this you would have to create a new tablespace with a large block size (32k). Then move your table to the newly created tablespace (alter table move). Depending on how big your long data are this should reduce/elimate the row chaining. But I have to admit that I have no idea if this way of reducing the chaining will realy help you.

If you want to understand why "chaining is often unavoidable for tables having LONG columns" I recommand you to have a look at
http://otn.oracle.com/docs/products/...schem.htm#2763
where it is written that:
...if all of a row's data cannot be inserted into a single data block ... Oracle stores the row using multiple row pieces. ... When Oracle must store a row in more than one row piece, it is chained across multiple blocks.