Hypoxic environments in the core of tumors can give rise to resistance against anticancer therapeutics. Oxygen-producing biomaterials may be able to improve chemotherapeutic efficiency by locally disrupting the hypoxic environment. We hypothesized that gellan gum hydrogels could be loaded with both a solid peroxide and the chemotherapeutic drug doxorubicin, to release both oxygen and doxorubicin simultaneously. We show that calcium peroxide physically cross-links gellan gum into a hydrogel, which when loaded with catalase raises the dissolved oxygen content of media for up to 64 h. Additionally, doxorubicin could be loaded into the hydrogel in situ, allowing release in well-defined quantities.