Marun oil field is one of the giant oil fields in southwest of Iran. It consists of two oil reservoirs and one gas reservoir named Asmari, Bangestan, and Khami, respectively. One of the major problems in this field is contamination of Asmari reservoir with H2S gas. The aim of this article was to study the trend and history of H2S spreading in Asmari reservoir of Marun oil field and also to investigate communication of Asmari reservoir layers via evaluation of fracture distribution, horizontal and vertical permeability distribution, and repeat formation test results. The results demonstrated good communication of layers in the center, especially in sectors 4 and 6 of the southern limb, central part of Asmari reservoir, due to higher fracture, higher permeability, and good pressure communication in these sectors. Moreover, the history of H2S concentration during time showed a decreasing trend while this contamination is spreading from the southeast to northwest of Asmari reservoir.