In a normal x-ray, only the luminal surface (blue arrows) should be visible outlined by gas. The serosal surface (orange) should not be visible as it is normally in contact with other intra-abdominal content of similar density (other loops of bowel, omentum, fluid). In this case, gas abuts the serosal surface rendering it visible.
As this film has been obtained supine (note absence of air-fluid levels), ascites pools in the paracolic gutters, with fluid mixed in with gas bubbles (green arrows).