Like for example ZG ( gold CBOT ) and GC( gold COMEX ) ... Same tick value.... Same instrument... It's not available anymore since there are bots but I'm sure there were opportunities in early days of electronic GC... It 's a bad example since this one would never last 30 minutes for sure, but there are.
Those I trade are not that straight forward ... Sometimes they involve 3 legs( calendar spreads ), one stock leg- one future leg... I've a spreadsheet that scan every market I know there may be opportunities.