"2,000 yen worth of gas please." usually we are in a hurry so short, to the point instructions are appropriate to use as long as you use the word "please" to make it polite.
"2,000 yen worth of gas please."
ガソリンを２０００円分お願いします。
通常私たちは急いでいるので短く、部分的な指示で言います。Please をつけている限り丁寧なフレーズになります。
You thought you had your credit card but you just remembered
- it was at home on the kitchen worktop.
You're low on fuel and there is a petrol station right ahead.
You rummage frantically through your coat pocket and find 2000 yen! You pull into the garage.
The pump attendant comes over to your car.
"Good evening sir."
"Good evening. Could I have 2000 yen worth of gas please?"
"Do you mean LPG gas?"
"NO, I just returned from the USA, sorry. They call petrol gas over there. What I really want is 2000 yen worth of petrol!"
"Oh, now I understand you. Sure thing!"
Gas (US) = petrol (UK)
クレジットカードを持っていたと思っていたけど、キッチンに忘れてきてしまった。
ガソリンは少ないけど、そこにガソスタがある。
コートのポケットを探すと2000円を発見した。
ガレージにいれて、定員がこちらに近づいてきた。
会話例
"Good evening sir."
こんばんわ。
"Good evening. Could I have 2000 yen worth of gas please?"
こんばんわ。2000円分ガスをください。
"Do you mean LPG gas?"
LPGガスでよろしいですか？
"NO, I just returned from the USA, sorry. They call petrol gas over there. What I really want is 2000 yen worth of petrol!"
いいえ、USAから戻ったんだ。ごめんね。彼らはPetrol gasといってたんだけど、自分が欲しいのは2000円分のPetrolなんだ。
"Oh, now I understand you. Sure thing!"
ああ、かしこまりました。もちろんです。
Gas (US) = petrol (UK)
When you're trying to tell the assistant at the garage that you want gas and for how much, you can simply say:
-I would like some gas for 2000 yen, please.
-Can I get gas for 2000 yen, please?
Please is there to be polite. You don't always have to say it, but it's preferable that you do.
ガソリンスタンドで、いくら分のガソリンが欲しいのかを伝える言い方です：
-I would like some gas for 2000 yen, please.
ガソリン2000円分ください。
-Can I get gas for 2000 yen, please?
ガソリン2000円分もらえますか？
「please」を使うと丁寧になります。必ず言わないといけない、というわけではないですが、使うことをお勧めします。
It is very important to exercise respect at every turn.
So, using the word 'please' will bring about good service from the attendant.
Using 'may' as in the second question is also a very polite request.
It will also bring about good service from the attendant.
"Please, can I have 2000 yen worth of gas."
This explains to them that you want to buy 2000 yen worth of gas.
"2000 yen, please. " Is a reply when asked how much gas you would like.
Please, can I have 2000 yen worth of gas.
これは、2000円分のガソリンを買いたいということです。
「2000 yen, please.」とは、どれくらいガソリンが欲しいかということを聞いたときの返事です。
日本 
アメリカ合衆国 
イギリス 
南アフリカ 
