Walmart partners with Instacart to test offering same-day delivery, starting in four markets across California and Oklahoma (Jessica Bursztynsky/CNBC)

Jessica Bursztynsky / CNBC:
Walmart partners with Instacart to test offering same-day delivery, starting in four markets across California and Oklahoma  —  - The partnership is currently in a pilot phase in four markets across California and Oklahoma.  — The move cements Instacart's hold over the online grocery delivery market.