  We develop the theory of Banach algebras whose multiplication (regarded as a
bilinear map) is open. We demonstrate that such algebras must have topological
stable rank 1, however the latter condition is strictly weaker and implies only
that products of non-empty open sets have non-empty interior. We then
investigate openness of convolution in semigroup algebras resolving in the
negative a problem of whether convolution in $\ell_1(\mathbb{N}_0)$ is open. By
appealing to ultraproduct techniques, we demonstrate that neither in
$\ell_1(\mathbb{Z})$ nor in $\ell_1(\mathbb Q)$ convolution is uniformly open.
The problem of openness of multiplication in Banach algebras of bounded
operators on Banach spaces and their Calkin algebras is also discussed.
