The Montana Rail Link leases its entire mainline from the BNSF. All branches were purchased by MRL but the main line was leased. The main reason stated by BN in 1987 for lease rather than sale was simple. The Northern Pacific at some point in the past sold bonds with a really long term...something like 50 or 75 years. These bonds didn't expire until 2047 and the mainline was the collteral for this transcation. Should NP-BN-BNSF default on these bonds, the bond holders could then foreclose on the mainline and sell it to recoup there money. If BN had sold the line, spent the cash, then in 10 years defaulted, the bond holders wouldn't have a guaranteed something to forceclose on. I heard, but I not positive, that BN or BNSF has since eliminated those bonds by whatever financial means it required.