Experts from the National Institute of Geophysics and Volcanology have been taking sample tests on gas escaping from a newly-formed geyser in the sea just off the port of Fiumicino.
It is the third incident of a geyser erupting in the Fiumicino area in the last month however the other two are located on land.
On 9 September a geyser, spotted late August on the boundary of Fiumicino international airport, turned into a "mini volcano" sending earth and carbon dioxide 5m into the air. On 24 September a natural gas geyser erupted at the end of Viale del Lago di Traiano.
The location of the sea geyser is where the port authority is carrying out underwater soundings, up to 40m in depth, for the construction of a commercial port. The mayor of Fiumicino, Esterino Montino, has conceded that the two events may be connected.