Unocal will buy 39% of shares tendered by holders.

The Los Angeles oil company said that it will begin issuing debt securities worth $72 per share within a week and that it expects the exchange to be completed by July 15. Slightly more than 151 million of Unocal’s 173 million outstanding shares were tendered in its offer to buy back 50 million shares--down from its earlier estimate of 154 million shares. Separately, Unocal Chairman Fred L. Hartley said in a speech Wednesday that the Reagan Administration’s tax reform proposal has thrown a cloud over Unocal’s plan to issue master limited partnership units. While the company still intends to form the partnership, he said, “there are tax questions that are bothering me.”