Air Products is making an unsolicited offer of about $5.1 billion in cash for smaller rival Airgas. The offer is worth about $60 a share and would represent a 38% premium on Thursday's closing price for Airgas' shares of $43.53. If the offer is rejected, Air Products could launch a hostile bid for Airgas, the New York Times and Wall Street Journal have reported.

The offer was made in a letter to Airgas' board of directors on Thursday after the CEOs of the two companies had previously discussed Air Products' interest in acquiring Airgas and after Air Products had made two written offers. According to the company, these offers and Air Products' requests to discuss them were rejected by Airgas.