Union Pacific is reportedly considering acquiring a rival railroad, sending shares of CSX and Norfolk Southern higher.

CSX has a $62.5 billion market capitalization, compared to $58.7 billion for Norfolk Southern. Union Pacific is the largest of the three S&P 500 railroad stocks, with a $138.1 billion market cap. BofA also cited CSX's internal improvements in the upgrade, according to The Fly investment site.

CSX Corp. stock is up on reports that Union Pacific is interested in buying the Jacksonville-headquartered railroad company. CSX Corp.’s stock rose to its highest level of the year July 17 after a report that Union Pacific Corp. is seeking to buy one of the two major eastern railroads, CSX or Norfolk Southern Corp.