a1 CSIRO Astronomy and Space Science, PO Box 76, Epping NSW 1710, Australia
a2 Astro Space Centre, Profsouznaya st. 84/32, 117997 Moscow, Russia
a3 School of Mathematics and Physics, University of Tasmania, GPO Box 252-37, Hobart, Tasmania 7000, Australia
a4 Macquarie University, Department of Physics and Engineering, NSW 2109, Australia
a5 Ural State University, Lenin ave. 51, 620083 Ekaterinburg, Russia
a6 Centre for Astronomy, School of Engineering and Physical Sciences, James Cook University, Townsville, QLD 4814, Australia
We review properties of all known collisionally pumped (class I) methanol maser series based on observations with the Australia Telescope Compact Array (ATCA) and the Mopra radio telescope. Masers at 36, 84, 44 and 95 GHz are most widespread, while 9.9, 25, 23.4 and 104 GHz masers are much rarer, tracing the most energetic shocks. A survey of many southern masers at 36 and 44 GHz suggests that these two transitions are highly complementary. The 23.4 GHz maser is a new type of rare class I methanol maser, detected only in two high-mass star-forming regions, G357.97-0.16 and G343.12-0.06, and showing a behaviour similar to 9.9, 25 and 104 GHz masers. Interferometric positions suggest that shocks responsible for class I masers could arise from a range of phenomena, not merely an outflow scenario. For example, some masers might be caused by interaction of an expanding Hii region with its surrounding molecular cloud. This has implications for evolutionary sequences incorporating class I methanol masers if they appear more than once during the evolution of the star-forming region. We also make predictions for candidate maser transitions in the ALMA frequency range.