Two shipowners exposed to the improving Jones Act tanker market with the same vessels are seeing their share prices diverge, raising questions about whether and when the gap will narrow.

New York-listed Overseas Ship­holding Group (OSG)’s shares have more than doubled in value since February, while stock in Oslo-­quoted American Shipping Company has climbed by less than one-fifth.

The contrast is attracting attention, given American Shipping’s 10-strong fleet is on bareboat charter to OSG with a profit share that is in the money.