* Unit taken out of production after vapor releases * Gulf Coast gasoline after CDU taken out of production * Unit was formally commissioned by refinery officials Thursday HOUSTON, June 4 (Reuters) - Motiva Enterprises newly commissioned 325,000 barrel per day (bpd) crude distillation unit at the 600,000 bpd Port Arthur, Texas, refinery was taken out of production following a malfunction early Monday, according to sources familiar with refinery operations. The unit was placed on circulation following vapor releases, the sources said. It could be returned to normal operation later on Monday. Gulf Coast gasoline differentials rose Monday morning as news of the Motiva outage permeated the market. Conventional M2 gasoline gained 2.00 cents per gallon to 9.50 cents under July RBOB futures on the New York Mercantile Exchange. A2 CBOB iniitally climbed 2.50 cents to 11.00 cents under, but later retreated to 12.00 cents under, up by 1.50 cents per gallon from Friday's levels. At ceremonies on Thursday, officials from joint venture Motiva and its owners Royal Dutch Shell Plc and Saudi Aramco formally commissioned the 325,000 bpd crude unit, which began production in late April. The crude unit, a delayed coking unit, hydrocracking and hydrotreating units and other ancillary units cost about $10 billion to build over five years. The new crude unit boosted the Port Arthur refinery to a crude oil refining capacity of 600,000 bpd, making the refinery the largest in the United States. A crude distillation unit does the initial refining of crude oil coming into a refinery and provides feedstock to all other units.