* Jupiter: The largest and most massive planet, composed mostly of hydrogen and helium with traces of other elements.

* Saturn: Known for its beautiful rings, Saturn is also primarily composed of hydrogen and helium.

* Uranus: An ice giant, Uranus has a thick atmosphere of hydrogen and helium but also has significant amounts of methane, water, and ammonia.

* Neptune: Similar to Uranus in composition, Neptune is an ice giant with a hydrogen and helium atmosphere and a large amount of heavier elements like water, methane, and ammonia.

While all four planets are considered gas giants, Jupiter and Saturn are the "gassiest" due to their composition being almost entirely hydrogen and helium. They have significantly less of the heavier elements found in Uranus and Neptune.

It's important to note that even though these planets are called "gas giants," they don't have a defined solid surface like Earth does. The gas just gets denser and denser as you go deeper into the planet, eventually transitioning into a liquid state.