Expected space consumption of skip lists What is the expected space used by the skip list after inserting $n$ elements?

I expect that in the worst case the space consumption may grow indeﬁnitely.

Wikipedia says space $O(n)$.

How can this be proven one way or another?
In this paper it is proven that there exists a constant $\alpha$ such that the probability of the space exceeding $\alpha n$, is less than $1/2^{\Omega(\sqrt{n})}$. Thefore, the more elements there are, the less likely it is to exceed this space bound.