Standard & Poor's Ratings Services said it placed its 'A-' long-term corporate credit ratings on Denmark-based energy companies Dong A/S and Elsam A/S on CreditWatch with negative implications.

The ratings action reflects the risk that Dong's potential cash acquisition of up to 76 percent of Elsam shares--including the preemption 35 percent stake held by Sweden-based utility Vattenfall AB (A-/Stable/A-2)--could result in...