TITLE: $G$-bundles on affine spaces
QUESTION [11 upvotes]: Let $G$ be a connected algebraic group. Is it true that every $G$-bundle on 
${\mathbb A}^n$ is trivial? What is the reference?
I am actually only interested in the case $n=2$.

REPLY [3 votes]: In characteristic $p$ you can make an easy counterexample with $n=1$, right? An exact sequence of commutative algebraic groups $0\to E\to X\to \mathbb A\to 0$ with $E$ an elliptic curve.