If the Oilers finish last overall, they will pick no worse than 2nd in the draft.
The NHL holds a lottery for the position, and the winner of the lottery moves up 4 positions in the draft, and no team can move down more than one spot. The lottery is heavily weighted in favour of the team that finishes 30th overall.
So, if the Oilers finish 30th overall, and the lottery is won by a team OTHER than those finishing in 26th, 27th, 28th, and 29th...........the Oilers will draft first.
So, if the Oilers finish 30th overall, and the lottery is won by a team that finished in 26th, 27th, 28th, and 29th...........that team will draft first, and the Oilers would drop a spot to 2nd.
So, at worst, the team finishing last overall would pick 2nd (barring of course any trades involving the Oilers first draft pick)