Depending on what year Jeep you have, it may cause the check engine light to come on. It won't effect how the engine runs but it will effect the emissions.
The 2012 Jeep Grand-Cherokee runs on flex-fuel (FFV).
The 2014 Jeep Grand-Cherokee runs on flex-fuel (FFV).
The 2013 Jeep Grand-Cherokee runs on flex-fuel (unleaded/E85).
The 2008 Jeep Wrangler runs on regular unleaded.
The 2013 Jeep Patriot runs on regular unleaded.
The 2004 Jeep Wrangler runs on regular unleaded.
The 2010 Jeep Patriot runs on regular unleaded.
The 2007 Jeep Patriot runs on regular unleaded.
The 2009 Jeep Compass runs on regular unleaded.
The 2008 Jeep Compass runs on regular unleaded.
The 2011 Jeep Wrangler runs on regular unleaded.
The 2002 Jeep Wrangler runs on regular unleaded.