Tablespace has 3 datafiles - import uses which?

[JMac]

I exported a db into a replacement database recently. The original database had one datafile per tablespace, but the new one has 3 per tablespace spread over 3 different disks.

Example: One TBS had 3 x 100mB files. The Import filled one file 100%, the others: 25% and 27% (I had expected an even spread of 50% for each datafile).

Another TBS - 3 x 400Mb. Had a spread over the disks of 73% - 24% and 26%

A third TBS - 3 x 350Mb had a spread of 21% - 47% - 21%

Can anyone xplain to me how Oracle decides which disks to use? Is Import different from the normal load balancing I might expect?

Its 9.2.0.1 on Win NT4 and the TBSs are locally managed with uniform extent sizes of 1Mb