If you've tried ordering groceries for delivery this week, it isn't you. In a coronavirus era, the old rules and expectations have been thrown out the window.

Getting online groceries delivered is currently a major challenge, as demand is overwhelming the companies that offer the services.

Many retail stores have closed, so many of us have turned to online shopping for food. Restaurants are serving the public with deliveries, but getting groceries ordered and delivered is hit and miss, at least according to USA TODAY tests Tuesday.

We tried shopping on e-commerce powerhouse Amazon and the company-owned Whole Foods Market website, which regularly touts online shopping, as well as competitors Walmart and Target, supermarket chain Vons, and supermarket delivery apps Peapod and Instacart.

Instacart

Instacart was most effective. The app serves as a service for 25,000 grocery stores, or half of America's markets, according to the company.

In our tests with Instacart, the order went through, with the promise of same-day delivery, within five hours of the order. Charges: $3.99 delivery fee, $2.00 "service" fee and $2 recommended tip for the driver.

But when we returned an hour later and tried to do another order, all deliveries were done for the day, and we were instructed to return, "at an earlier time."

"Based on the current surge in demand, customers can expect to see delivery availability vary across stores during the busiest request windows," Instacart said. "Delivery windows are specific to individual store volume and shopper availability. As availability opens up for an individual store, customers will see these delivery windows become available on the Instacart marketplace."

Amazon

Shopping for food on Amazon proved fruitless. The company, which told shoppers Tuesday it was delaying deliveries for nonessential items to prioritize household staples and medical supplies, for much of the day wasn't offering delivery for food through its Amazon Fresh program, nor Whole Foods. For members of the Amazon Prime expedited shipping and entertainment service, same-day delivery is usually free.

The old days:How Amazon Prime Now compares to Instacart, Walmart and other grocery delivery rivals

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But after we filled the cart, Amazon had no available delivery dates through April, while Whole Foods depended upon when you ordered. At 9 a.m., there were no delivery times available, but after trying again an hour later, there were two slots available on the same day. A third attempt at 1:45 p.m. showed no delivery spots available.

In a statement, Amazon said it's experienced an increase in online grocery orders, "and are working around the clock to continue to deliver grocery orders to customers as quickly as possible."

Peapod

Peapod, which serves the East Coast markets like Stop and Shop and Food Lion, had one available delivery date available when we tested Tuesday for a New Jersey delivery: March 30. Peapod charged a $10 delivery fee.

Walmart and Target

Orders at Walmart and Target, the largest big-box retailers, were equally frustrating. Both stores instructed the shopper to come in and pick up the items instead of having them delivered, something that would be quite hard to do considering the quarantine status in many cities. By playing around and choosing different items, Target agreed to deliver, through the Shipt app, but with a four-week trial for a service that costs $99 yearly.

However, when we declined and chose the $9.99 delivery charge instead, Target said all same-day shipping slots for today and Wednesday were taken, with no offers of other dates.

For the items Walmart didn't direct shoppers to in-store pickup, we were offered a Monday delivery and $5.99 delivery fee for soda and cereal.

Walmart spokeswoman Molly Blakeman said the company is trying to keep up with "unprecedented demand," that consumers should shop early and come back often. Her tip: Try ordering from different local Walmarts until they find a store that will fulfill the orders. "Keep checking back."

Vons

Our local Vons market (which is owned by the national Albertsons chain) had no delivery dates available, but it would allow consumers to shop online and select the orders and have everything ready for pickup at a later date. For a $4.95 fee. The earliest we could get for pickup from a Tuesday order at noon was 7 p.m. on Thursday.

The good news: The food will be waiting, and there will be less contact in the store with others, plus everything will be prepaid.

But will there be a space in the parking lot?

Follow USA TODAY's Jefferson Graham (@jeffersongraham) on Twitter