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The grocery wars continue to heat up.

As US households continue to grapple with rising costs for gas, housing, and insurance, they're increasingly looking for savings on groceries.

That's giving value-focused retailers like Walmart and Costco a major leg up over more traditional grocery giants like Kroger and Albertsons.

Data released this week from consumer analytics firm Numerator showed warehouse giant Costco overtook Kroger's dollar share of US retail food and beverage sales. Costco has steadily gained share over the last two years as both Kroger and Albertsons shrank their positions.

The estimates are based on the last 12 months of sales, and show Costco's share ticking up to 8.4%, a half percentage point higher than the same period a year earlier.

And even though Walmart has long held the largest share of grocery spending, it managed to gain 0.2 percentage points to capture 20.3% of sales in the period.

By comparison, Kroger's share fell by 0.2 percentage points…