Si la oferta sigue mañana, compraré otra botella de agua y dos yogures.

In Spanish, after si when you mean a real or likely future condition, you normally use the present tense, not the future:

• Si la oferta sigue mañana... = If the offer is still on tomorrow...

English often uses the present here too: If the offer continues tomorrow...

Using seguirá after si would sound unnatural in standard Spanish for this kind of condition. A very common pattern is:

• Si + present, future
• Si tengo tiempo, iré.
• Si hace buen tiempo, saldremos.

So this sentence follows that pattern perfectly.

Because it expresses what the speaker will do if the condition is met.

The sentence has two parts:

• Si la oferta sigue mañana = the condition
• compraré otra botella de agua y dos yogures = the result

Since the result is in the future, Spanish uses the future tense:

• compraré = I will buy

This is a very common structure:

• Si + present, future
• Si puedo, te llamaré.
• Si vienen, prepararemos la cena.

Yes. Continuar and seguir can both work here.

• La oferta sigue mañana = The offer is still on tomorrow / continues tomorrow
• La oferta continúa mañana = The offer continues tomorrow

Seguir often sounds a bit more natural and conversational in everyday speech. It can also carry the idea of still being in effect. In the context of a sale or promotion, sigue is very idiomatic.

Here, oferta most likely means a special offer, promotion, or sale price, not just a general “offer” in the English sense.

So Si la oferta sigue mañana... means something like:

• If the promotion is still on tomorrow...
• If the special offer is still available tomorrow...

In shops and supermarkets in Spain, oferta is very commonly used for discounted products.

Because Spanish usually doesn’t need subject pronouns when the verb ending already shows who the subject is.

• compraré clearly means I will buy

So yo compraré is grammatically correct, but usually unnecessary unless you want emphasis or contrast:

• Yo compraré otra botella, pero tú no.
  = I’ll buy another bottle, but you won’t.

In a neutral sentence, just compraré sounds more natural.

In Spanish, otro / otra normally replaces the indefinite article un / una.

So you say:

• otra botella = another bottle
• otro yogur = another yogurt

Not:

• una otra botella ❌

This is different from English, where another historically includes the idea of an + other. In Spanish, otra already does that job by itself.

Spanish often uses de to connect two nouns where English uses one noun to modify another.

So:

• botella de agua = bottle of water
• vaso de leche = glass of milk
• taza de café = cup of coffee

English can say water bottle, but in this sentence the meaning is probably a bottle of water to drink, not an empty container designed for water. So botella de agua is the natural choice.

Yes. In Spain, yogur is the standard singular form, and yogures is the plural.

• un yogur
• dos yogures

You may also sometimes see yoghurt or yogurt, but yogur is the usual standard Spanish form and is very common in Spain.

No. Numbers like dos, tres, cuatro, etc. do not change for gender or number.

So you say:

• dos yogures
• dos botellas
• dos libros

By contrast, words like otro / otra do agree:

• otro yogur
• otra botella

So in this sentence:

• otra agrees with botella (feminine singular)
• dos stays the same

Yes. Both are possible.

• compraré = simple future
• voy a comprar = near future / going to buy

So you could say:

• Si la oferta sigue mañana, voy a comprar otra botella de agua y dos yogures.

In everyday spoken Spanish, ir a + infinitive is very common. But compraré is also completely natural and often sounds a bit more concise or definite.

Because mañana is an adverb of time, and its position is flexible. In this sentence, sigue mañana sounds natural and clear.

You could also say:

• Si mañana sigue la oferta...

That version puts more emphasis on tomorrow.

So both are possible, but they feel slightly different in focus:

• Si la oferta sigue mañana... → focus on whether the offer continues
• Si mañana sigue la oferta... → focus more on tomorrow

It is a real or possible future condition.

The speaker thinks it is genuinely possible that the offer will still be available tomorrow. That is why Spanish uses:

• si + present
• future in the main clause

Compare:

• Si la oferta sigue mañana, compraré...
  = real possibility

A more hypothetical or unlikely idea would use a different pattern:

• Si la oferta siguiera mañana, compraría...

That means something more like If the offer were still on tomorrow, I would buy..., which sounds more remote or less likely.

A natural pronunciation in Peninsular Spanish would be approximately:

Si la o-FER-ta SI-ghe ma-NYA-na, com-pra-RÉ O-tra bo-TE-lla de A-gua y dos yo-GU-res.

A few useful points:

• oferta: stress on fer
• sigue: the u is silent, so it sounds like SI-ghe / SI-ge
• mañana: the ñ is like ny in canyon
• compraré: stress on the last syllable because of the written accent
• botella: stress on te
• yogures: stress on gu

In most of Spain, g before e in sigue sounds like a throaty sound, not like the English g in go.