Check your owner's manual. Lancers are offered with several different engine types each which may require different fuel types. To determine yours it would be necessary to know the year and trim/options.
Generally speaking, however, most Lancer models run on Regular.
The 2009 Mitsubishi Lancer runs on regular unleaded.
The 2006 Mitsubishi Lancer runs on regular unleaded.
The 2004 Mitsubishi Lancer runs on regular unleaded.
The 2005 Mitsubishi Lancer runs on regular unleaded.
The 2002 Mitsubishi Lancer runs on regular unleaded.
The 2008 Mitsubishi Lancer runs on regular unleaded.
The 2014 Mitsubishi Lancer runs on regular unleaded.
The 2003 Mitsubishi Lancer runs on regular unleaded.
The 2010 Mitsubishi Lancer runs on regular unleaded.
The 2013 Mitsubishi Lancer runs on regular unleaded.
The 2012 Mitsubishi Lancer runs on regular unleaded.
The 2011 Mitsubishi Lancer runs on regular unleaded.