Gases can be compressed easily because there is a large amount of space between the individual molecules, which are very active and move around at high speed. When gas is compressed, the particles are forced much closer together, allowing a huge amount of particles to fit in a small space.
One common use of compressed gas is in scuba diving tanks, where oxygen is compressed to the point that 600 liters can fit into a three liter tank. As gas particles move so rapidly, they seek areas of less concentration to give them more area to move around. This leads to compressed gas rapidly escaping a container if it is not properly sealed.
Of the three basic states of matter, the particles in gas are much further apart than in liquid or solid matter. Some liquids can be slightly compressed, while most solids cannot be compressed at all, except for a small group that includes synthetic and natural rubbers. In addition to solids, liquids and gases, scientists have also discovered two other forms of matter: plasma and Bose-Einstein condensate. Plasma occurs naturally in lightning and is made in laboratories to be used in televisions and other electronics. Bose-Einstein condensate was discovered in 1995 and can only be made in a lab under extremely cold temperatures.