I have been in restaurant rest rooms that used vessel sinks nested in something vs sitting on the counter, I do not recall. Maybe one used pebbles in the sink?

Is this for looks or a DIY repair?

Ick.

"Want to know if a vessel sink can be mounted over the oval hole instead of replacing the counters."

Probably, but not cost effectively. I get this call, or one similar, regularly. I just can't buy a sink, install it, and reconnect the plumbing as cheaply as you can call a Big Box store and have them replace top and all.

Fitting the special faucet for a vessel sink may require drilling new holes in your countertop, then covering the old holes with finish-matched covers. The drain hole for the old sink may not line up with the vessel sink drain hole. The whole thing may look kind of kludgy.

I am on a budget.

Most of us are. What is your budget? How much are you spending on the sink? And the new faucet because the old one probably isn't going to work with a vessel sink?

Are people still installing vessel sinks?

Vessel sinks in general are a design style that takes extra effort to look good IMO and the execution rarely lives up to the idea IMPO. Complicating the installation as you describe OP sounds like a potential disaster.

Since you like a vessel sink, spend the extra time saving to get a professional install the right way (not over an existing molded bath sink) so you can enjoy your choice rather than have a compromise that could very well cost you more money.

Vessel sinks have an advantage in a public restroom. Often regular sink usage will result in wet counters, sometimes with wet counter rims. Lean against that wet counter and one’s pants get wet.

Happened to me at a local restaurant, then later to the president of the company I worked for at the same restaurant during a work lunch. This was in the 80’s, when “we” wore suits to work.

I would not waste the time and extra effort.

If you want a vessel sink:

1. You can contact a local fabricator and give them your counter measurements. They can give you an estimate to cut down and refinish a remnant piece for you to fit a vessel sink.

2. Make sure you have the height. Vanities with vessel sinks are shorter than the standard 34 1/2" Tall that are common now a days. The vanity would have to be around 28 1/2 - 30" (depending on the height of sink) tall so with the counter and new vessel sink you would equal to 36" to top rim.

3 You will have to change the faucet to a taller faucet specific for a vessel sink. Standard faucets are not usable for this application.

You might be able to cut out the moulded sink and install a half recessed vessel sink similar to the one you see below, but sizes and cuts will be tricky. Additionally, you will have to use the same holes for the faucet, unless you select a sink size that will cover over the old holes.

WHY, just why? Vessels are so OUT

I like vessel sinks in the right place but not jerry rigged where you are planning . Get a new counter top and do what you like

How about a drop-in sink with pre-cut faucet hole(s)? Cut out enough of the countertop to fit the sink. If it didn't work you might be out less than $100.

Love hearing these things were a fad that is waning!! They never made sense to me. Good call on the faucet issue. A prefab counter/sink combo is super cheap--compared to many vessels. Your budget far exceeds mine it would seem.

Thanks to all for the advice

SOME vessel sink styles are dated…. But the concept has evolved from
A simple bowl on a counter top to sleek and minimalist beauties, and are absolutely sleek and gorgeous!! Vessel sinks encompass a variety of design styles and materials, and are one of the two most popular design options of modern high end bathrooms- the other being large integrated (usually floating) sink styles. Check out Toto, for example, and design-centered websites, even new high end home walkthroughs. Under mount sinks are still popular and lovely of course, showing off the beautiful quartz, granite, etc countertops they are tucked into. That being said, they often feel “cramped” for hand washing, and yes, wet countertops are a frequent complaint. One solution for that is to have a larger (not standard) undermount sink installed. Although, those who don’t like the idea of germs lurking on the undermounts underside, are also not fans. 🤷‍♀️Conversely, The “vessel” sinks additional width and height is a plus. Taller countertops are considered more luxurious- and are certainly more ergonomic for many adults. If your countertop is an average height- the vessel sink on top is sort a little “cheat” to getting that additional height! Not having to “lean” so much to wash one’s hands- so much better. You WILL need a taller faucet- which is another great way to incorporate additional design elements (and possibly touch-less technology) and upgrade your sink area. Yes, it’s probably best to remove the whole old sink and countertop, (and maybe the vanity)…. But this is how whole bathroom remodels start! 🙂 😁so, “on a budget”- I would suggest researching each aspect of your idea- (YouTube ) take measurements (including reading the specifications of your the new sink you want to install) and definitely consider the plumbing configuration, and/or consult with a plumber. With enough research and planning- You can certainly replace your old sink with a vessel one over the top- and have an amazing looking result …where there is a will (and some tools)…there is a way! BUT, the devil IS in the details- think it through, write down the supplies needed, cost of these items, the effort involved- and how many friends you need to involve- 😉and then you will know if you “really” want to do this project…. A poorly done project doesn’t add value- it diminishes it- and usually leads to costly repairs later.

@Silver cottage: "Although, those who don’t like the idea of germs lurking on the undermounts underside, are also not fans."

People don't like germs on the undersides of sinks? The undersides?

"Vessel sinks...are one of the two most popular design options of modern high end bathrooms"

There is a one-to-one correlation* between those for whom vessel sinks are popular and those with maids.

*and causation