Walmart and Instacart have joined forces to offer same-day delivery in four U.S. markets, the latest play by a major grocery chain to partner with the delivery service. Walmart will be available through Instacart in Los Angeles, San Francisco and San Diego as well as Tulsa, Oklahoma as part of its initial launch, which begins on Tuesday, a spokesperson for Instacart . Instacart says the partnership will give customers access to items ranging from groceries, alcohol, pantry staples, and home decor "in as fast as an hour."