Method and system for improving azimuth distribution. The system includes plural streamers towed by a streamer vessel; a central source towed by the streamer vessel; first and second front sources located in front of the plural streamers along a traveling direction of the streamer vessel; and first and second tail sources located behind of the plural streamers along the traveling direction. The offset distance between the first and second tail sources, along a cross-line direction, is larger than an offset distance between the first and second front sources.